Sheet metal parts in the form of extrusions and shaped sheet are often used in aircraft structures for structural assemblies. These metal component parts are relatively thin, usually about 3/16″ maximum, and most typically between about ⅛″ to about 1/16″ in thickness. The component parts may be thinner than 1/16″, the thickness being dictated by the application. These structural assemblies can be intricate internal assemblies or assemblies such as fuselage structures, wing structures, nacelles or thrust reversers. In order to properly assemble these structures, it is necessary to further form the extrusions and shaped sheet to have joints that permit proper fit-up as well as strength. These joints are formed by using a die assembly to form a joggle in the extrusion or shaped sheet.
A joggle is an offset in a flat plane consisting of at least two bends in opposite directions in which material is displaced into a new plane that is parallel to the original plane. The joggle forms a new plane from the original material that is substantially parallel to the plane of the original shaped sheet or extrusion. Joggles are formed by placing the shaped sheet metal or extrusions in a die to form the desired joint configuration. These joggles are then assembled to similar or identical joggles in mating parts that allow for proper fit-up and assembly of the mating parts. Typically, the dies are modular die systems. While the shaped sheet or extrusions may have joggles formed by cold working, that is, forming the joggle at ambient temperature, the joggles more frequently are formed by heating the workpiece to elevated temperatures by using heated dies.
Many of the sheet metal parts utilized in aircraft applications include titanium and titanium alloys as well as aluminum and aluminum based alloys such as aluminum alloy designated as 7075. Joggles are hot formed in extrusions and shaped sheet of this alloy by manually positioning the extrusion or shaped sheet in contact with a heated die in a forming press. The dies are modular and are interchangeable, the specific die system used depending upon the extrusion or shaped sheet that is supplied and the location and shape of the joggle required. The length of the extrusion or shaped sheet into which the joggle is to be formed is not restricted, although the joggle is typically formed near the end of the part. Typically, a joggle is formed within about two feet of one end of the extrusion or shaped sheet, as this is the location of fit-up with a mating part. However, the die system and forming press may be designed to form a joggle at greater distances from an end of the extrusion or shaped sheet.
The current practice for aligning an extrusion, shaped sheet or other workpiece in a forming press is for the operator to manually position the part inside of a preselected heated die. A combination square having a right angle and a scale along at least one edge is positioned against a die surface, and the workpiece is positioned adjacent to, or in contact with, the end of the scale on the combination square to allow the operator to properly align the workpiece in the forming press. This method is both inefficient and hazardous. It is hazardous as it requires the operator to perform hand alignment of the workpiece inside or adjacent to heating dies that have been heated to an elevated temperature, typically about 300° F.-370° F. for aluminum alloy 7075. The temperature will vary depending upon the alloy used, and may be higher or lower, but will always be sufficiently high for forming and capable of causing burns to a careless operator. In addition, proper alignment may entail the operator placing his/her hands within the die assemblies of the forming press, thereby exposing a careless operator to potential injury by placing hands within pinch points. In addition to the dangers with the present system, it is also inaccurate. The workpiece is aligned visually and by hand by an operator against a scale having linear gradations that are 1/32″ (0.031″) or 1/64″ (0.015″) apart, requiring the operator to estimate the correct location of the workpiece within the die. Furthermore, as the workpiece becomes longer and with a portion of the workpiece extending beyond the die, it becomes more difficult for the operator to correctly estimate the location of the portion of the workpiece into which the joggle is to be formed as the operator must attempt to align a location marker applied to the workpiece with a parting line in the die that is used to form the joggle. Not only is the system limited by the instrumentation, but also additional error easily can be introduced by failure of the operator to properly align the workpiece against the scale. Clearly, due to the inherent inaccuracies, the current system can reasonably be controlled from about 1/64″ to about 1/16″ depending upon the skill of the operator and the degree of care expended by the operator. The current system does not produce repeatable results within tolerance limits typically desired for fit-up and assembly of aircraft components. When controlled tolerances are required, additional manufacturing operations must be included.
Currently, when accuracy is required in the location of a joggle, a workpiece having an excess of material is positioned in the die assembly and the joggle is formed in the workpiece in the conventional manner. After removal of the joggled workpiece from the die assembly, the excess material is then machined from the workpiece and the workpiece is measured to determine the proper location of the joggle, and re-machined as required.
What is needed is an accurate, repeatable system to position a workpiece formed of extruded metal or shaped sheet metal in a die system for forming joggles that reduces the inaccuracies inherent in the current system in aligning the workpiece, allowing for repeatable and precise alignment of the workpiece in relation to the die system.